The present invention relates to a composite refractory structure constituted by an electro-cast refractory component based on ceramic oxides, refractories and other materials, and mineral oxides, which includes at least one variously shaped structural element that is highly resistant to corrosion and/or erosion produced by molten baths and in particular by baths of molten glass and the like.
The scope of the present invention also includes a process for producing said monolithic composite refractory structure, which can be used to make furnaces for glassmaking and particularly in the regions of the furnace that are most intensely subjected to the corrosive action of molten glass.
It is known that the technology for building glassmaking furnaces uses appropriately assembled monolithic elements made of electro-cast refractory material which are usually termed "electro-cast blocks".
These electro-cast blocks are produced in various shapes, sizes, kinds, and qualities, and are all obtained by casting a mixture of molten refractory oxides in a three-phase electric-arc furnace, as disclosed in Italian patent Application 19461 A/87 of Feb. 23, 1987.
The molten mixture is cast into appropriately designed and shaped molds, where it undergoes a first partial cooling and assumes the intended shape. The electro-cast refractory material then completes its cooling cycle in controlled conditions; at the end of this cycle, it is usually machined and finished mechanically.
This final product is commonly termed "electro-cast refractory block".
It is also known that the electro-cast refractory material is attacked during use, as a consequence of the various mechanical, physical, and chemical conditions that occur in each part of the furnace.
The attack to which the electro-cast refractory is subjected wears it away. The extent of the wear determines the duty life of the blocks of electro-cast material and substantially determines the duty life of the glass furnace.
The wear of blocks of electro-cast material is different according to their quality, type, and location in the furnace. In fact, it is known that there are areas in the furnace where wear is more intense than in others. It is widely acknowledged that among the most intense wear which occurs, there is the wear in the electro-cast blocks that compose the throat of the furnace, in particular the throat cover block at the glass inlet, the weir wall, or in the area of the blocks that is technically defined as "flux line" or "metal line".
In order to extend the life of a glass furnace as much as possible, good practice selects and assembles together electro-cast refractories having different qualities and properties in order to balance the extent of wear in every part of the furnace.
In the production of glass furnaces it is in fact now common to simultaneously have blocks of electro-cast refractory having different chemical compositions (Al.sub.2 O.sub.3 --ZrO.sub.2 --SiO.sub.2, alpha and beta Al.sub.2 O.sub.2, ZrO.sub.2, Al.sub.2 O.sub.2 --Cr.sub.2 O.sub.3 --SiO.sub.2 --ZrO.sub.2, etcetera), located in specific areas depending on the quality and type of glass produced and on the stresses that they must withstand.
In the known art, despite using different materials, a satisfactory balance between the wear of the various regions of the glass furnace has not yet been achieved, and therefore the optimum life of said furnace is still not achieved due to the early wear of some parts thereof.
In order to reduce the effects of this disparity in wear and ensure the maximum operating life of the furnace, one generally resorts to other solutions of a mechanical type, such as cooling the structure from outside, or to repairs of the most intensely worn regions while the furnace is hot and running. Known from EP-A-008261 is a refractory block, for steel furnaces, having a rectangular cross-section and a metal or graphite insert. The insert has an X-shaped cross-section extending along the diagonals of the rectangular cross-section of the refractory block, for facilitating cooling and thereby prolonging the working life of the block. However, the block is not designed for prolonged contact with molten material and has no means for preventing excessive wear of the block upon coming into contact with molten material.